Process for producing purified aqueous hydrogen peroxide solution and apparatus

ABSTRACT

A process for producing a purified aqueous hydrogen peroxide solution, comprising passing a charged aqueous hydrogen peroxide solution containing impurities through a purifier tower packed with an ion exchange resin, a chelate resin or an adsorption resin to thereby purify the charged aqueous hydrogen peroxide solution, wherein there are provided a feed pump of given output capable of causing the charged aqueous hydrogen peroxide solution to flow to the purifier tower and further a flow sensor capable of sensing a flow rate of charged aqueous hydrogen peroxide solution being fed to the purifier tower and wherein the output of the feed pump is controlled in cooperation with the flow sensor so as to bring the charged aqueous hydrogen peroxide solution into contact with the ion exchange resin, chelate resin or adsorption resin while maintaining the flow of charged aqueous hydrogen peroxide solution at a constant rate. In this process, not only can remaining of bubbles in the purifier tower be avoided but also pressure and temperature increases can be prevented in the purification operation, so that the aqueous hydrogen peroxide solution can be brought into contact with the ion exchange resin, etc. safely and efficiently.

FIELD OF THE INVENTION

[0001] The present invention relates to a process for producing apurified aqueous hydrogen peroxide solution and an apparatus therefor.More particularly, the present invention is concerned with a process forproducing a high-purity aqueous hydrogen peroxide solution, wherebyimpurities can be removed from a charged (crude) aqueous hydrogenperoxide solution with high reproducibility, and an apparatus therefor.

BACKGROUND OF THE INVENTION

[0002] An aqueous hydrogen peroxide solution is widely used in manyfields, for example, for bleaching paper and pulp and as a component inchemical polishing fluids. In recent years, the aqueous hydrogenperoxide solution has increasingly been used in the electronic industry,for example, as a cleaning agent for silicon wafers and as a cleaningagent in production processes of semiconductors. Accordingly, there is ademand for an aqueous hydrogen peroxide solution of enhanced quality inpurity as obtained by minimizing the content of various impurities inthe aqueous hydrogen peroxide solution.

[0003] Generally, hydrogen peroxide is now produced exclusively by theanthraquinone process. In the anthraquinone process, first, a derivativeof anthraquinone, such as a 2-alkylanthraquinone, is hydrogenated intoanthrahydroquinone in the presence of a hydrogenation catalyst in awater-insoluble solvent. Subsequently, the catalyst is removed, and thereaction product is oxidized with air. Thus, not only is the original2-alkylanthraquinone regenerated but also hydrogen peroxide is producedat the same time. The produced hydrogen peroxide is extracted from theoxidation product with water to thereby obtain an aqueous solutioncontaining hydrogen peroxide. This process is generally known as theanthraquinone autoxidation process. The aqueous hydrogen peroxidesolution produced by the anthraquinone autoxidation process containsinorganic ion/compound impurities, such as Al, Fe, Cr, Na and Si,attributed to, for example, the materials constituting the apparatus.Therefore, the aqueous hydrogen peroxide solution is subjected topurification operation for removing such impurities to thereby attain ahigh purity in accordance with the required quality in particular use.

[0004] Especially in the electronic industry, an extremely high purityis required for the aqueous hydrogen peroxide solution. It is requiredthat, in the aqueous hydrogen peroxide solution, the content of organicimpurities be not greater than 10 ppm and the content of metal ionimpurities be not greater than 1 ppb. For the removal of impurities fromthe aqueous hydrogen peroxide solution, it is generally known to employan ion exchange resin, a chelate resin, an adsorption resin or the like.When the removal of impurities is carried out on an industrial scalewith the use of such a resin, there is commonly employed the continuousliquid pass method (tower process) which ensures high operationefficiency and high removing efficiency.

[0005] The purification of aqueous hydrogen peroxide solution by thetower process involves such a problem that bubbles are formed byautolysis of hydrogen peroxide, which is a property peculiar to hydrogenperoxide, and the bubbles stick to resin circumstances to thereby lowerpurification efficiency, i.e., impurity removing efficiency.

[0006] As a means for solving this problem, for example, Japanese PatentLaid-open Publication No. 9(1997)-77504 discloses a process in which anupper part of an ion exchange resin tower is pressurized so as toincrease the solubility of bubbles formed by autolysis of hydrogenperoxide, thereby eliminating bubbles from the purifier tower.

[0007] However, the process disclosed in Japanese Patent Laid-openPublication No. 9(1997)-77504 has a drawback in that the content ofmetal ion impurities in purified aqueous hydrogen peroxide solution is 1ppb, which is not necessarily satisfactory level, and that qualityreproducibility is poor. Moreover, when the operation time is prolonged,it may occur that bubbles are accumulated in the ion exchange resintower with the result that the area of contact between ion exchangeresin and aqueous hydrogen peroxide solution is decreased, or thecomplete adsorption band (part where the adsorption of impurity ions hasbeen completed) or exchange band (part where ion exchange is beingperformed) of ion exchange resin is disordered. Consequently,satisfactory removal of impurities may be inhibited, and further thepassing of aqueous hydrogen peroxide solution may be hindered to therebybring about problems such as pressurization and temperature rise withinthe ion exchange resin tower.

[0008] In these circumstances, the inventors have made extensive andintensive studies with a view toward solving the above problems. As aresult, it has been found that, when the aqueous hydrogen peroxidesolution is purified by controlling the output of a feed pump forcharged aqueous hydrogen peroxide solution in cooperation with a flowsensor capable of sensing a flow rate of charged aqueous hydrogenperoxide solution being fed to a purifier tower so as to bring thecharged aqueous hydrogen peroxide solution into contact with an ionexchange resin while maintaining the flow of charged aqueous hydrogenperoxide solution at a constant rate, the impurities of aqueous hydrogenperoxide solution can be removed to the order of ppt (parts per 10¹²) Ithas also been found that, in this purification process, not only is thereproducibility of impurity removing level very high but also thepressurization and temperature rise during purification can be avoidedto thereby realize a safe purification of aqueous hydrogen peroxidesolution. The present invention has been completed on the basis of thesefindings.

[0009] When the aqueous hydrogen peroxide solution is purified bybringing the aqueous hydrogen peroxide solution into contact with an ionexchange resin, a chelate resin or an adsorption resin while maintainingthe flow of aqueous hydrogen peroxide solution being fed to the purifiertower at a constant rate according to the present invention, sticking ofbubbles to the ion exchange resin, etc. within the purifier tower can besuppressed. Further, in this purification process, not only can theleaving of bubbles in the purifier tower be avoided but also disorderingof the complete adsorption band or ion exchange band can be suppressed.Still further, in this purification process, the aqueous hydrogenperoxide solution can be easily passed through the purifier tower. Thus,a purification efficiency of aqueous hydrogen peroxide solution is high.

[0010] It is an object of the present invention to provide a process forproducing a purified aqueous hydrogen peroxide solution, which processis free from any disordering of ion exchange band during purification,free from bubbles remaining in a purifier tower and free from anypressurization or temperature rise within the purifier tower to therebyenable effecting a safe and efficient contact of aqueous hydrogenperoxide solution with an ion exchange resin or the like. It is anotherobject of the present invention to provide an apparatus for producing apurified aqueous hydrogen peroxide solution, which apparatus is suitablefor the above process.

SUMMARY OF THE INVENTION

[0011] The process for producing a purified aqueous hydrogen peroxidesolution according to one aspect of the present invention comprisespassing a charged aqueous hydrogen peroxide solution containingimpurities through a purifier tower packed with an ion exchange resin, achelate resin or an adsorption resin to thereby purify the chargedaqueous hydrogen peroxide solution, wherein there are provided a feedpump of given output capable of causing the charged aqueous hydrogenperoxide solution to flow to the purifier tower and further a flowsensor capable of sensing a flow rate of charged aqueous hydrogenperoxide solution being fed to the purifier tower and wherein the outputof the feed pump is controlled in cooperation with the flow sensor so asto bring the charged aqueous hydrogen peroxide solution into contactwith the ion exchange resin, chelate resin or adsorption resin whilemaintaining the flow of charged aqueous hydrogen peroxide solution at aconstant rate. In this process, it is preferred that the output of thefeed pump for the charged aqueous hydrogen peroxide solution becontrolled by means of an inverter.

[0012] The apparatus for producing a purified aqueous hydrogen peroxidesolution according to another aspect of the present invention comprisesat least one purifier tower packed with an ion exchange resin, a chelateresin or an adsorption resin, through which a charged aqueous hydrogenperoxide solution containing impurities is passed so as to effectcontact thereof with the ion exchange resin, chelate resin or adsorptionresin, thereby purifying the charged aqueous hydrogen peroxide solution,

[0013] which apparatus further comprises:

[0014] a feed pump of given output capable of causing the chargedaqueous hydrogen peroxide solution to flow to the purifier tower,

[0015] a flow sensor capable of sensing a flow rate of charged aqueoushydrogen peroxide solution being fed to the purifier tower by means ofthe feed pump, and

[0016] a flow control unit capable of controlling the output of the feedpump on the basis of a detection result of the flow sensor so as tomaintain the flow of charged aqueous hydrogen peroxide solution beingfed to the purifier tower at a constant rate.

[0017] When control is effected so as to maintain the flow of aqueoushydrogen peroxide solution at a constant rate as aforementioned, theleaving of gas in the purifier tower packed with an ion exchange resincan be avoided. Further, disordering of ion exchange band can beavoided, and an impurity ion adsorption layer (ion exchange band) can beformed perpendicularly to the flow rate and sharply. Thus, a lowering ofpurification efficiency can be avoided.

[0018] The flow rate of aqueous hydrogen peroxide solution being fedinto the purifier tower is preferably 5 to 40 hr⁻¹ in terms of spacevelocity. The flow rate of aqueous hydrogen peroxide solution ispreferably controlled so that its variation falls within the range of±2.5%.

[0019] In the process for producing a purified aqueous hydrogen peroxidesolution according to the present invention, it is preferred that anypart brought into contact with the aqueous hydrogen peroxide solution becomposed of a fluororesin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a schematic diagram showing the flow of operation of theprocess for producing a purified aqueous hydrogen peroxide solutionaccording to the present invention;

[0021]FIG. 2 is a schematic diagram of a flange as a constituent of astrainer for use in a purifier tower to be installed in the process forproducing a purified aqueous hydrogen peroxide solution according to thepresent invention;

[0022]FIG. 3 is a schematic diagram showing the flow of operation of theprocess for producing a purified aqueous hydrogen peroxide solution,performed in Example 1; and

[0023]FIG. 4 is a schematic diagram showing the flow of operation of theprocess for producing a purified aqueous hydrogen peroxide solution,performed in Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The process for producing a purified aqueous hydrogen peroxidesolution according to the present invention will be described in detailbelow. Herein, %, ppm, ppb and ppt are all on the weight basis.

[0025] In the present invention, the process for producing a purifiedaqueous hydrogen peroxide solution according to one aspect of thepresent invention comprises passing a charged aqueous hydrogen peroxidesolution containing impurities through a purifier tower packed with anion exchange resin, a chelate resin or an adsorption resin to therebypurify the charged aqueous hydrogen peroxide solution, wherein there areprovided a feed pump of given output capable of causing the chargedaqueous hydrogen peroxide solution to flow to the purifier tower andfurther a flow sensor capable of sensing a flow rate of charged aqueoushydrogen peroxide solution being fed to the purifier tower and whereinthe output of the feed pump is controlled in cooperation with the flowsensor so as to bring the charged aqueous hydrogen peroxide solutioninto contact with the ion exchange resin, chelate resin or adsorptionresin while maintaining the flow of charged aqueous hydrogen peroxidesolution at a constant rate.

[0026] This invention will be specified with reference to the flowdiagram of FIG. 1. FIG. 1 is a flow diagram showing one mode of processfor producing a purified aqueous hydrogen peroxide solution according tothe present invention. In FIG. 1, numerals 11, 13 denote lines; numeral12 a purifier tower; numeral 14 a liquid feed pump; numeral 15 aninverter; numeral 16 a flow sensor; numeral 17 a pressure sensor;numeral 18 a temperature sensor; and numeral 19 a level sensor.

[0027] A charged aqueous hydrogen peroxide solution is fed through line11 into purifier tower 12 by means of liquid feed pump 14. The aqueoushydrogen peroxide solution is brought into contact with an ion exchangeresin in the purifier tower 12, drawn from the purifier tower 12 andpassed through line 13 into other purifier tower(s) for contact with anion exchange resin. The thus purified aqueous hydrogen peroxide solutionis collected in a tank, subjected to concentration adjustment andproduct inspection, stocked, packed and delivered.

[0028] As the charged aqueous hydrogen peroxide solution which can beemployed in the present invention, there can be mentioned those producedby known processes, such as the anthraquinone autoxidation process andthe direct synthesis process in which hydrogen is directly reacted withoxygen.

[0029] The charged aqueous hydrogen peroxide solution generally containsmetal ion impurities on the order of parts per billion (ppb) to tens ofparts per million (ppm). As impurities contained in the charged aqueoushydrogen peroxide solution, there can be mentioned metal ion impuritiessuch as those of Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Fe, Ga,Ge, In, K, Li, Mg, Mo, Na, Nb, Ni, Pb, Pd, Pt, Sb, Sr, Ta, Ti, Tl, V, Znand Zr, and further silicon oxide impurities and organic impurities.These impurities are attributed to, for example, residues of catalysts,etc. used in the production of aqueous hydrogen peroxide solution by theanthraquinone process, anthraquinone decomposition products, solventsused in the production of aqueous hydrogen peroxide solution, water usedin production (e.g., extraction, distillation and dilution).of anaqueous hydrogen peroxide, floating dust in air and materials ofproduction apparatus.

[0030] As aforementioned, in the present invention, the charged aqueoushydrogen peroxide solution is fed through the line 11 into the purifiertower 12 by means of the liquid feed pump 14. The line 11 is fitted withflow sensor 16. Signal from the flow sensor 16 is sensed by inverter 15.The inverter 15 controls the output of the liquid feed pump 14 so as tomaintain the flow of aqueous hydrogen peroxide solution at a constantrate.

[0031] The flow sensor 16 is appropriately selected from among those ofthe vortex type, the paddle type, the electromagnetic type, theultrasonic type and other types. All of these flow sensors measure theflow velocity and flow quantity and feeds signals back to the inverterfor controlling of the output of the liquid feed pump. Among the flowsensors, those of the vortex type and the paddle type are preferred.

[0032] In the present invention, controlling is effected so that theflow of aqueous hydrogen peroxide solution being fed into the purifiertower is maintained at a constant rate. Thus, sticking of formed bubblesto, for example, the ion exchange resin and consequently remaining inthe purifier tower can be avoided. As a result, a decrease of the areaof contact of aqueous hydrogen peroxide solution with the ion exchangeresin or the like and also disordering of the above complete adsorptionband or exchange band can be avoided for a prolonged period of time.Therefore, the impurity removing efficiency can be held high for aprolonged period of time.

[0033] In the present invention, the space velocity (SV) at which theaqueous hydrogen peroxide solution is passed through the purifier tower12 is preferably in the range of 5 to 40 hr⁻¹, still preferably 10 to 30hr⁻¹. It is preferred that controlling be effected so that the variationof flow rate of aqueous hydrogen peroxide solution falls within therange of ±2.5%. This flow control enables highly efficiently expellingand removing of bubbles without remaining thereof in the purifier tower.

[0034] The aqueous hydrogen peroxide solution introduced in the purifiertower 12 is passed through a center nozzle (not shown) provided insidethe purifier tower so that the aqueous hydrogen peroxide solution iscaused to uniformly flow downward. The ion exchange resin, chelate resinor adsorption resin is preferably packed in the purifier tower so as tooccupy 40 to 80%, still preferably 45 to 75%, of the internal volume ofthe purifier tower.

[0035] Referring to FIG. 1, the purifier tower 12 is generally fittedwith level sensors 19 arranged with a given distance vertically so as tomaintain the liquid level in order to prevent drying of the ion exchangeresin or the like. As the level sensor, use can be made of those of thephotovoltaic type and the electrostatic capacity type. Of these, thelevel sensor of the electrostatic capacity type is preferred. The levelsensors 19 sense the presence of liquid as a signal. when the liquidlevel is below the lower limit of level sensor, that is, when the liquidsurface is detected by the under level sensor 19, the internal pressureof the purifier tower 12 is increased to excess, so that a separatelevel control unit (not shown) is operated. Thus, bleeder valve 20disposed at the top of the purifier tower is opened while a valvedisposed at the bottom of the purifier tower is closed to thereby reducethe internal pressure of the purifier tower through the bleeder valve20. As a result, the liquid surface is returned to normal.

[0036] On the other hand, when the liquid surface is sensed at the upperlimit of level sensor, that is, when the liquid surface is detected bythe upper level sensor 19, the internal pressure of the purifier tower12 is decreased to excess, so that a separate level control unit (notshown) is operated. Thus, the bleeder valve 20 disposed at the top ofthe purifier tower is closed while the valve disposed at the bottom ofthe purifier tower is opened. As a result, the liquid surface isreturned to normal.

[0037] In the present invention, it is preferred that the pipes forliquid feeding and the internal wall of the purifier tower be composedof a fluororesin. That is, it is preferred that the parts brought intocontact with the aqueous hydrogen peroxide solution be composed of afluororesin. When these liquid contact parts are composed of afluororesin, mixing of impurities from constituent members can beinhibited. In the prior art, hard glass, quartz, vinyl chloride resin,acrylic resin, FRP and steel having linings made from urethane, etc. arecommonly employed as materials of purification apparatus, and it hasoccurred that impurities are leached from such materials into an aqueoushydrogen peroxide solution.

[0038] The practical method of constituting the liquid contact parts bya fluororesin comprises, for example, preparing the member per se from afluororesin, or lining or coating a stainless steel or the like with afluororesin.

[0039] As the fluororesin, generally, polytetrafluoroethylene resin(PTFE) and tetrafluoroethylene/perfluoroalkyl vinyl ether copolymerresins (PFA) can appropriately be employed because these are free frommetal leaching and because these are stable and are not deteriorated inhydrogen peroxide. In recent years, in accordance with the progress ofprocessing technology, a stainless steel as a base material can be linedor coated with such fluororesins. Now, large-size lined (coated) vesselsand large-size lined (coated) tower, equipment, piping, etc. are beingfabricated, and these are utilized without any problem even undersuperatmospheric or reduced pressure conditions. As other availablefluororesins, there can be mentioned, for example,tetrafluoroethylene/hexafluoropropylene copolymer resin (FEP),polytrifluorochloroethylene resin (PCTFE) andtetrafluoroethylene/ethylene copolymer (ETFE).

[0040] In particular, when the internal wall of the purifier tower 12 iscomposed of a fluororesin, the aqueous hydrogen peroxide solutionlocated in the neighborhood of the internal wall surface is forcedtoward the center due to the water repellency of the fluororesin. Thus,short pass (short cut) of aqueous hydrogen peroxide solution on theinternal wall surface (short pass of aqueous hydrogen peroxide solutionalong the internal wall surface) can be suppressed, i.e., passing ofaqueous hydrogen peroxide solution without contacting with the ionexchange resin or the like can be avoided. As a result, the removal ofimpurities can be accomplished efficiently.

[0041] Depending on the type of ion exchange resin, chelate resin oradsorption resin, the purifier tower 12, upstream thereof, may beprovided with a heat exchanger for cooling. It is also preferred thatthe heat exchanger be composed of a fluororesin.

[0042] The purifier tower 12 is preferably one capable of resisting apressure of about 0.3 MPa/cm². The purifier tower 12 is fitted withpressure sensor 17, and bleeding or other operation is performedaccording to necessity.

[0043] A pressure sensor of the diaphragm type can be used, wherein apressure change is transmitted by a diaphragm to a pressure receivingpart where the pressure change is converted to a signal. Specifically,when the pressure is increased, for example, when the pressure of thepurifier tower packed with an anion resin exceeds 0.2 MPa, thepossibility of decomposition of hydrogen peroxide is high. The pressureincrease is sensed by the pressure sensor 17, and a separate pressurecontrol unit (not shown) is operated. Thus, the liquid feed pump 14 isstopped, and the bleeder valve 20 disposed at the top of the purifiertower is opened. Further, cooled ultra-pure water is fed into thepurifier tower, thereby discontinuing the production of purified aqueoushydrogen peroxide solution.

[0044] Furthermore, the purifier tower 12 is fitted with temperaturesensor 18, which is capable of sensing any heat build-up associated withprocessing of aqueous hydrogen peroxide solution so as to effectappropriate cooling. A temperature sensor of the thermocouple type orthe resistance bulb type can be used, wherein an electromotive force ora resistance value is changed by temperature and the change thereof isconverted to a signal. For example, when the temperature inside thepurifier tower exceeds a given value, the decomposition of aqueoushydrogen peroxide solution is initiated. Thus, any internal temperatureincrease of the purifier tower is sensed by the temperature sensor 18,and a separate temperature control unit (not shown) is operated.Accordingly, the liquid feed pump 14 is stopped, and the bleeder valve20 disposed at the top of the purifier tower is opened. Further, cooledultra-pure water is fed into the purifier tower, thereby discontinuingthe production of purified aqueous hydrogen peroxide solution.

[0045] The bottom part of the purifier tower 12 is fitted with astrainer (not shown). The strainer comprises a filter (not shown) and,disposed thereunder, flange 30 as shown in FIG. 2.

[0046] The flange 30 has vertically through liquid drawoff port 32 atthe center thereof and further has a plurality of substantially annularopen grooves 34 formed in the form of concentric circles with a givenspacing from the liquid drawoff port 32. The open grooves 34 areprovided with communicating open grooves 36 spaced at a given angle inthe radial direction, which communicate with the liquid drawoff port 32provided in the center of the flange 30.

[0047] Accordingly, the aqueous hydrogen peroxide solution having passedthrough the filter is led through the open grooves 34 and thecommunicating open grooves 36 and discharged outside from the liquiddrawoff port 32 in the form of substantially a laminar flow.

[0048] With respect to the open grooves 34 and the communicating opengrooves 36, the groove spacing, spaced angle and groove depth can beappropriately varied and are not particularly limited.

[0049] It is preferred that the total void ratio of filter and flangeopening be in the range of 50 to 70%, especially 55 to 65%. When thetotal void ratio is in this range, the aqueous hydrogen peroxidesolution can be passed through the purifier tower in the form of alaminar flow with the result that the aqueous hydrogen peroxide solutioncan be brought into uniform contact with the ion exchange resin, chelateresin or adsorption resin. The above strainer separates the purifiedaqueous hydrogen peroxide solution from the ion exchange resin, chelateresin or adsorption resin.

[0050] In the present invention, as mentioned above, the purifier toweris packed with the ion exchange resin (such as anion exchange resin orcation exchange resin), chelate resin or adsorption resin, depending onthe purpose. Also, the purifier tower can be packed with a mixed bedcomposed of an anion exchange resin and a cation exchange resin.

[0051] As the cation exchange resin for use in the present invention,there can be mentioned H⁺-type cation exchange resin known as a stronglyacidic cation exchange resin. Among various strongly acidic cationexchange resins, a strongly acidic cation exchange resin of networkmolecular structure comprising a crosslinked styrene/divinylbenzenecopolymer wherein sulfonate groups are introduced is generallypreferred. For example, PK216, SKLB and IR-120B are used as the aboveH⁺-type strongly acidic cation exchange resin.

[0052] The H⁺-type cation exchange resin is preferably one regeneratedby repeating at least twice a step comprising treating the cationexchange resin with a downflow of aqueous solution of inorganic acid(regenerant) and thereafter washing the cation exchange resin with anupflow of ultra-pure water. In the present invention, it is preferredthat the regeneration be conducted by repeating the downflow of anaqueous solution of regenerant followed by the upflow of ultra-purewater at least twice, especially 2 to 12 times.

[0053] The treatment of cation exchange resin with an aqueous solutionof regenerant is generally performed by passing the aqueous solution ofregenerant through the cation exchange resin, discharging the aqueoussolution of regenerant and thereafter washing the cation exchange resinwith ultra-pure water. In the present invention, it is preferred thatthe cycle of regenerant passing and ultra-pure water washing be repeatedat least twice. When the passing of an aqueous solution of inorganicacid followed by passing of ultra-pure water is repeated, not only canthe regeneration be accomplished efficiently and uniformly but also,because of the shrinkage/swelling of cation exchange resin, washing canbe effected to the inside of cation exchange resin.

[0054] As the inorganic acid, there can be employed any of commoninorganic acids such as sulfuric acid and hydrochloric acid. Theconcentration of inorganic acid in the aqueous regenerant solution ispreferably in the range of 5 to 15% by weight, still preferably 5 to 12%by weight. It is preferred that the regenerant be used in an amount ofat least 3 times, especially 4 to 12 times, the quantity (volume) ofcation exchange resin to be treated.

[0055] The regenerant is generally passed downward at a SV (spacevelocity) of 1 to 5 hr⁻¹ and at a BV (bed volume, indicating what volumeof aqueous hydrogen peroxide solution is treated per volume of ionexchange resin) of 0.5 to 1 L/L-R. The subsequent washing is performedby passing ultra-pure water upward at a SV of 10 to 30 hr⁻¹ and at a BVof 0.1 to 0.5 L/L-R.

[0056] After the regenerant passing followed by ultra-pure waterpassing, an ultra-pure water washing cycle comprising downward passing(downflow) of ultra-pure water and upward passing (upflow) of ultra-purewater is repeated 4 to 9 times to thereby effect complete washing of theregenerated ion exchange resin. It is preferred that the upflow ofultra-pure water be performed at a SV of 10 to 30 hr⁻¹ and at a BV of 3to 5 L/L-R and that the downflow of ultra-pure water be also performedat a SV of 10 to 30 hr⁻¹ and at a BV of 3 to 5 L/L-R. The washing ispreferably performed with 30 to 60 volumes of ultra-pure water pervolume of the resin.

[0057] As the anion exchange resin for use in the present invention,there can be mentioned those in the form of carbonate ions, hydrogencarbonate ions, hydroxide ions, fluoride ions and other ions.

[0058] As these anion exchange resins, generally, use can be made of,for example, strongly basic resins obtained by chloromethylating acrosslinked styrene/divinylbenzene copolymer and aminating thechloromethylation product with trimethylamine or dimethylethanolamineinto a quaternary salt; weakly basic resins comprising a crosslinkedstyrene/divinylbenzene copolymer having a primary or tertiary amine asan exchange group; resins comprising a crosslinked acrylic acid polymerhaving a tertiary amine as an exchange group; and pyridine type anionexchange resins comprising a polymer having an unsubstituted orsubstituted pyridyl group. of these, strongly basic anion exchangeresins having a quaternary ammonium group are preferred. Various anionexchange resins having a quaternary ammonium group are commerciallyavailable, representative examples of which include Diaion (trade name)PA series (for example, PA316 and PA416) and SA series (for example,SA10A and SA20A) and Amberlite (trade name) IRA series (for example,IRA-400, IRA-410, IRA-900 and IRA-904). These resins are generallyavailable on the market in the form of chloride ions.

[0059] The regenerant for anion exchange resin can be appropriatelyselected depending on the type of target ions. When the anion exchangeresin is in the form of carbonate ions or hydrogen carbonate ions, aknown carbonate or bicarbonate salt such as sodium carbonate, sodiumbicarbonate, potassium carbonate or potassium bicarbonate can be used asthe regenerant. When the anion exchange resin is in the form ofhydroxide ions, a strong alkali such as sodium hydroxide or potassiumhydroxide can be used as the regenerant. Further, when the anionexchange resin is in the form of fluoride ions, sodium fluoride,potassium fluoride or ammonium fluoride can be used as the regenerant.

[0060] The anion exchange resin is preferably one regenerated byrepeating at least twice a step comprising treating the above anionexchange resin with a downflow of regenerant and thereafter washing theanion exchange resin with an upflow of ultra-pure water. In the presentinvention, it is preferred that the regeneration be conducted byrepeating cycle comprising downflow of an aqueous solution of regenerantfollowed by the upflow of ultra-pure water at least twice, especially 2to 12 times. The treatment of anion exchange resin with an aqueoussolution of regenerant is generally performed by passing the aqueoussolution of regenerant through the anion exchange resin, discharging theaqueous solution of regenerant and thereafter washing the anion exchangeresin with ultra-pure water. In the present invention, it is preferredthat the cycle of regenerant passing and ultra-pure water washing berepeated at least twice. When the passing of an aqueous solution ofregenerant followed by passing of ultra-pure water is repeated, not onlycan the regeneration be accomplished efficiently and uniformly but also,because of the shrinkage/swelling of anion exchange resin, washing canbe effected to the inside of anion exchange resin.

[0061] The appropriate salt concentration of the aqueous regenerantsolution is in the range of 2 to 10% by weight, preferably 2 to 8% byweight, when the anion exchange resin is in the form of hydroxide ions;5 to 15% by weight, preferably 5 to 12% by weight, when the anionexchange resin is in the form of carbonate or hydrogen carbonate ions;and 1 to 4% by weight, preferably 2 to 4% by weight, when the anionexchange resin is in the form of fluoride ions. It is preferred that theaqueous solution of regenerant be used in an amount of at least 3 times,especially 4 to 12 times, the quantity (volume) of anion exchange resinto be treated.

[0062] The regenerant is generally passed downward at a sv (spacevelocity) of 1 to 5 hr⁻¹ and at a BV of 0.5 to 1 L/L-R. The subsequentwashing is performed by passing ultra-pure water upward at a SV of 10 to30 hr⁻¹ and at a BV of 0.1 to 0.5 L/L-R.

[0063] After the regenerant passing followed by ultra-pure waterpassing, an ultra-pure water washing cycle comprising downflow ofultra-pure water and upflow of ultra-pure water is repeated 4 to 9 timesto thereby effect complete washing of the regenerated ion exchangeresin. It is preferred that the upward passing of ultra-pure water beperformed at a SV of 10 to 30 hr⁻¹ and at a BV of 3 to 5 L/L-R and thatthe downward passing of ultra-pure water be also performed at a SV of 10to 30 hr⁻¹ and at a BV of 3 to 5 L/L-R. The washing is preferablyperformed with 30 to 60 volumes of ultra-pure water per volume of theresin.

[0064] From the viewpoint of oxidation deterioration of resin andsafety, it is preferred that the contact of the anion exchange resinwith the aqueous hydrogen peroxide solution be performed at lowtemperature. In particular, more H⁺ than formed by dissociation ofhydrogen peroxide may be contained in the aqueous hydrogen peroxidesolution having been treated with the H⁺-type cation exchange resin in aprevious stage, and the H⁺ may induce an exothermic neutralizationreaction with anion exchange groups CO₃ ²⁻ and HCO₃ ⁻. Therefore, whenthe aqueous hydrogen peroxide solution is treated with the anionexchange resin, it is preferred that cooling be effected to 5° C. orbelow in advance.

[0065] In the process of the present invention, it is preferred that aplurality of towers packed with the above ion exchange resin beconnected each other in series when the charged aqueous hydrogenperoxide solution is purified.

[0066] For example, preferred combinations of ion exchange resin towersare:

[0067] (1) cation exchange resin tower→anion exchange resin tower;

[0068] (2) cation exchange resin tower→anion exchange resin tower→cationexchange resin tower; and

[0069] (3) anion exchange resin tower→cation exchange resin tower.

[0070] Of these, the combination of cation exchange resin tower→anionexchange resin tower→cation exchange resin tower is especiallypreferred. In particular, impurities can be most effectively removed bytreating the charged aqueous hydrogen peroxide solution with the use ofthe combination of H⁺-type cation exchange resin tower→fluoride-formanion exchange resin tower→carbonate or bicarbonate-form anion exchangeresin tower→H⁺-type cation exchange resin tower.

[0071] In the use of a plurality of ion exchange resin towers incombination, it is satisfactory to dispose the flow sensor and the flowcontrol unit such as the liquid feed pump 14 may be arranged at a linefor feeding the charged aqueous hydrogen peroxide solution to the firstpurifier tower. However, other ion exchange resin towers can also befitted with the above flow sensor and flow control unit.

[0072] Minute amounts of Na⁺, K⁺, Al³⁺ and other matter contained in thecharged aqueous hydrogen peroxide solution as impurities can be removedby sequentially bringing the charged aqueous hydrogen peroxide solutioninto contact with the cation exchange resin, the anion exchange resinand the cation exchange resin. Therefore, the removal of metal ionimpurities can be accomplished to an extremely high level (order of pptor sub-ppt). When use is made of the anion exchange resin in thefluoride form, silicon oxide impurities can be removed from the aqueoushydrogen peroxide solution. Using the anion exchange resin in the formof carbonate ions or hydrogen carbonate ions is preferred from theviewpoint that the counter ions to Na⁺, K⁺ and Al³⁺ to be removed arecarbonate ions or hydrogen carbonate ions, these being converted tocarbon dioxide after cation exchange and evaporated with the result thatthese do not remain in the aqueous hydrogen peroxide solution.

[0073] Packing the purifier tower with the chelate resin or adsorptionresin in place of the above ion exchange resin enables effectivelyremoving impurities of the charged aqueous hydrogen peroxide solutionwhose removal ratio is low with the use of ion exchange resin, such asiron ions, Al ions and organic impurities.

[0074] The chelate resin is not limited as long as the resin exhibits achelate force to metal ions, and can be, for example, any ofiminodiacetic acid type, polyamine type and phosphonic acid type resins.In particular, phosphonic acid type chelate resins can preferably beused.

[0075] The phosphonic acid type chelate resins are chelate resinswherein a functional group having a phosphonic acid group is introduced.Especially preferred use is made of iminomethylenephosphonic acid typeand iminodi(methylenephosphonic acid) type chelate resins having a groupcomprising a nitrogen atom and, bonded thereto via a methylene group, aphosphonic acid group, represented by the formula—N(CH₂PO₃H₂)_(n)H_(2−n) wherein n is 1 or 2. Any of the phosphonic acidtype chelate resins, although generally used with its phosphonic acidgroup being in the form of a free acid, can also be used with itsphosphonic acid group being in the form of a salt such as an ammoniumsalt. The phosphonic acid type chelate resins are especially preferredin practical application from the viewpoint that, even if used in thepurification of aqueous hydrogen peroxide solution for a prolongedperiod of time, deterioration thereof is slight.

[0076] Porous resins having no ion exchange capability are used as theadsorption resin. The porous resins are, for example, resins composed ofa styrene/divinylbenzene copolymer and having no ion exchange group. Itis preferred that the porous resins have a specific surface area(measured in accordance with the BET method using N₂) of about 200 toabout 900 m²/g, especially 400 to 900 m²/g, on the basis of dry resin.Further, it is preferred that the pores be continuous and that theporous resins have a pore volume (measured by the mercury penetrationmethod) of about 0.6 to about 1.2 ml/g, especially 0.7 to 1.1 ml/g, onthe basis of dry resin. These porous resins can be, for example, resinsobtained by polymerizing styrene and crosslinking the polymer withdivinylbenzene to thereby form a network molecular structure. As suchadsorption resins, there can be mentioned, for example, Amberlite (tradename, produced by Rohm & Haas) XAD-2 and XAD-4, and HP10, HP20, HP21,HP30, HP40, HP50, SP800 and SP900 produced by Mitsubishi ChemicalCorporation, Ltd.

[0077] As the adsorption resin, halogenated porous resins can be used.Suitable examples of the halogenated porous resins include ahalogenation product of a crosslinked polymer from an aromatic monovinylmonomer such as styrene or vinyltoluene and an aromatic polyvinylmonomer such as divinylbenzene or trivinylbenzene; a crosslinked polymerfrom a halogenated aromatic monovinyl monomer such as monochlorostyreneor monobromostyrene and an aromatic polyvinyl monomer; and a crosslinkedpolymer from a halogenated aromatic monovinyl monomer, an aromaticmonovinyl monomer and an aromatic polyvinyl monomer. Among thesehalogenated porous resins, halogenation products of astyrene/divinylbenzene copolymer are especially preferred. As such,there can be mentioned, for example, Sepabeads SP207 (trade name)composed of a brominated styrene/divinylbenzene copolymer and having aspecific gravity of about 1.2. Furthermore, a crosslinked polymer froman aromatic monovinyl monomer and an aromatic polyvinyl monomer, whereina hydrophilic group such as a hydroxyl group, a chloroalkyl group or ahydroxyalkyl group is introduced, can also be used as the adsorptionresin.

[0078] The chloroalkyl group is represented by the formula:—(CH₂)_(n)Cl, and the hydroxyalkyl group is represented by the formula:—(CH₂)_(n)OH. When the linear chain is long, the hydrophilicity is low.Therefore, practically, it is preferred that n be in the range of 1 to5. Such a resin is commercially available. As such, there is known, forexample, Bofazit EP 63 (trade name, produced by Bayer).

[0079] Organic impurities and other impurities can be highly effectivelyremoved from the aqueous hydrogen peroxide solution by carrying out theabove purification process, thereby the amount of total organic carbon(TOC) can be reduced.

[0080] The impurities of the charged aqueous hydrogen peroxide solutioncan be more effectively removed by combining the treatment using thechelate resin and the adsorption resin with the treatment using the ionexchange resin described earlier.

[0081] In the process for producing purified hydrogen peroxide accordingto the present invention, the above purifier towers may be used alone orin combination. In the use of purifier towers in combination, forexample, the charged aqueous hydrogen peroxide solution may be treatedfirst with the adsorption resin tower (purifier tower packed withadsorption resin), subsequently with the chelate resin tower (purifiertower packed with chelate resin) and thereafter with the ion exchangeresin tower (purifier tower packed with ion exchange resin).Alternatively, the charged aqueous hydrogen peroxide solution may betreated first with the ion exchange resin tower, subsequently with theadsorption resin tower and thereafter with the chelate resin tower. Thecombination of adsorption resin tower→H⁺-type cation exchange resintower→fluoride-form anion exchange resin tower→carbonate orbicarbonate-form anion exchange resin tower→H⁺- type cation exchangeresin tower is especially preferred. In the use of this combination, theimpurity level of the aqueous hydrogen peroxide solution can beminimized.

[0082] In the use of the chelate resin tower, adsorption resin tower andion exchange resin tower in combination, the liquid feed pump 14 andflow sensor 16 may be disposed upstream of each of the purifier towers,or may be disposed only upstream of the purifier tower through which theaqueous hydrogen peroxide solution is first passed.

[0083] It is especially preferred that the liquid feed pump 14 bedisposed upstream of the adsorption resin tower and upstream of the ionexchange resin tower. Specifically, in the use of the combination ofadsorption resin tower→H⁺-type cation exchange resin tower→fluoride-formanion exchange resin tower→carbonate or bicarbonate-form anion exchangeresin tower→H⁺-type cation exchange resin tower, it is preferred thatthe liquid feed pump 14 be disposed where the aqueous hydrogen peroxidesolution is fed to the adsorption resin tower and where the aqueoushydrogen peroxide solution having been treated with the adsorption resintower is fed to the H⁺-type cation exchange resin tower.

[0084] In the present invention, prior to the above purificationoperation by means of purifier tower(s), it is preferred that acoagulant be added to the charged aqueous hydrogen peroxide solution andpassed through a superfine filter to thereby remove insoluble metal ionimpurities contained in the aqueous hydrogen peroxide solution as solidimpurities. This filtration is preferably performed before the treatmentof aqueous hydrogen peroxide solution with the ion exchange resin. Inthe treatment using the adsorption resin tower, the filtration may beperformed before that treatment, or after that treatment. However,filtering before the treatment with the adsorption resin tower ispreferred because impurities can be removed with extremely highefficiency.

[0085] These insoluble metal ion impurities, like the soluble metal ionimpurities, are attributed to water used in production, floating dustand materials of production apparatus.

[0086] The coagulant is added to coagulate insoluble metal ionimpurities in the aqueous hydrogen peroxide solution so that they can beseparated by filtration. Generally, a phosphorous compound is used asthe coagulant. As the phosphorous compound, there can preferably be usedat least one phosphorous compound selected from the group consisting ofphosphoric acid, polyphosphoric acid, acid sodium pyrophosphate,aminotri(methylenephosphonic acid) and its salts,ethylenediaminetetra(methylenephosphonic acid) and its salts.

[0087] After the addition of the phosphorous compound, it is generallypreferred that the mixture be aged for at least one day, especially oneto five days. The aging may be carried out with or without stirring. Byvirtue of this aging, insoluble metal ion impurities in the aqueoushydrogen peroxide solution are flocculated and grown to filteredaggregation/growth to such an extent that they can be separated byfiltration.

[0088] The average pore diameter of the superfine filter for use in thefiltration is preferably 0.2 μm or less, still preferably 0.1 μm orless. The material constituting the superfine filter is not particularlylimited as long as no components leached into the aqueous hydrogenperoxide solution are contained therein, and is, for example, selectedfrom among fluororesins, polyolefin resins (e.g., polyethylene orpolypropylene), polysulfone resins and polycarbonate resins. Of these,fluororesins are preferred.

[0089] According to necessity, ultra-pure water may be added to the thusobtained aqueous hydrogen peroxide solution to thereby adjust theconcentration of hydrogen peroxide therein. Suitable ultra-pure water isone from which impurities have been removed to a desirably high degree.

[0090] As a result of the above purification operations, there can beobtained the highly purified aqueous hydrogen peroxide solution whereofthe impurity concentration has been reduced to ppt level or itsvicinity.

[0091] Furthermore, in the present invention, use can be made of thecharged aqueous hydrogen peroxide solution from which organic impuritieshave been removed to a high degree by known methods. Also, from thehighly purified aqueous hydrogen peroxide solution obtained by theprocess of the present invention, organic impurities may be furtherremoved by known methods. As known methods for removing organicimpurities, there can be mentioned, for example, distillation, use of anultrafilter membrane filter and use of a reverse osmosis membrane. Thecombination of these methods with the process of the present inventionenables producing the purified aqueous hydrogen peroxide solution whoseimpurity content is extremely low.

[0092] In the present invention, the leaving of gas in the purifiertower packed with the ion exchange resin can be avoided. Further,disordering of ion exchange band can be avoided, and the impurity ionadsorption layer (ion exchange band) can be formed perpendicularly andsharply to the flow direction. Accordingly, impurities can beeffectively removed from the charged aqueous hydrogen peroxide solutionto thereby enable obtaining the purified aqueous hydrogen peroxidesolution of extremely high quality. Moreover, the process of the presentinvention is safe, realizes high purification efficiency for aqueoushydrogen peroxide solution, exhibits high reproducibility with respectto the content of impurities, and is stable.

EXAMPLE

[0093] The present invention will further be illustrated below withreference to the following Example which in no way limits the scope ofthe invention.

[0094] Herein, metal ion impurities were measured by the flamelessatomic absorption spectroscopy, the ICP-AES method and the ICP-MSmethod. The ppm, ppb and ppt are all on the weight basis.

Example 1

[0095] Acid sodium pyrophosphate was added to a 60.1% by weight aqueoushydrogen peroxide solution containing metal ion impurities as listed inTable 1 below so that the concentration of acid sodium pyrophosphate was0.070 g/lit. The mixture was allowed to stand still for 3 days tothereby effect aging, and passed through a filter of 0.1 μm average porediameter. The ratio of metal atom Al as a component of the metal ionimpurities to P atom as a component of the added acid sodiumpyrophosphate (atomic ratio of Al/P) was 0.039.

[0096] The thus filtered aqueous hydrogen peroxide solution was purifiedby sequentially passing the same through, referring to FIG. 3, afirst-stage H⁺-type cation exchange resin tower, a heat exchanger, abicarbonate-ion-form anion exchange resin tower and a second-stageH⁺-type cation exchange resin tower while controlling a liquid feed pumpin cooperation with a flow sensor so as to maintain the flow spacevelocity (SV) at a constant rate of 15 hr⁻¹. In each of the purifiertowers, the aqueous hydrogen peroxide solution was caused to flowdownward (downflow), and the liquid level was controlled so that theliquid surface was held above the ion exchange resin layer. The passingof the aqueous hydrogen peroxide solution through thebicarbonate-ion-form anion exchange resin tower was carried out whilecooling the aqueous hydrogen peroxide solution to −3° C. by means of theheat exchanger.

[0097] The regeneration of the above ion exchange resins was performedwith the use of another ion exchange tower (regeneration tower) disposedseparate from the aqueous hydrogen peroxide solution purifier towers.

[0098] A product of regeneration of used SK1B was utilized as thefirst-stage and second-stage H⁺-type cation exchange resins. A 10% byweight aqueous hydrochloric acid solution was utilized as theregenerant. The regeneration of the cation exchange resin was carriedout by packing the cation exchange resin into a regeneration towerdifferent from the purifier towers and by repeating 10 times a stepcomprising downflow of the aqueous regenerant solution through the towerat a SV of 2.25 hr⁻¹ and at a BV of 0.75 L/L-R, discontinuing thepassing of the aqueous regenerant solution and upflow of ultra-purewater through the tower at a SV of 13.2 hr⁻¹ and at a BV of 0.3 L/L-R.Thereafter, ultra-pure water washing of the cation exchange resin wascarried out by repeating 6 times a cycle comprising downward passingultra-pure water through the tower at a SV of 13.2 hr⁻¹ and at a BV of3.3 L/L-R and upflow of ultra-pure water through the tower at the sameSV and BV. Thus, the regeneration of the H⁺-type cation exchange resinwas completed.

[0099] A product of regeneration of spent SA20A was utilized as thebicarbonate-ion-form anion exchange resin. The used anion exchange resinwas first regenerated with sodium hydroxide. A 5% by weight aqueoussodium hydroxide solution was utilized as the regenerant. Theregeneration of the anion exchange resin was also carried out by packingthe anion exchange resin into a regeneration tower different from thepurifier towers and by repeating 6 times a step comprising downflow ofthe aqueous regenerant solution through the tower at a SV of 2.25 hr⁻¹and at a BV of 0.75 L/L-R, discontinuing the passing of the aqueousregenerant solution and upflow of ultra-pure water through the tower ata SV of 13.2 hr⁻¹ and at a BV of 0.3 L/L-R. Thereafter, ultra-pure waterwashing of the anion exchange resin was carried out by repeating 5 timesa cycle comprising downward passing ultra-pure water through the towerat a SV of 13.2 hr⁻¹ and at a BV of 3.3 L/L-R and upflow of ultra-purewater through the tower at the same SV and BV. Thus, there was obtainedOH⁻-type anion exchange resin.

[0100] Subsequently, this OH⁻-type anion exchange resin was regeneratedwith sodium bicarbonate. A 8% by weight aqueous sodium bicarbonatesolution was utilized as the regenerant. The regeneration with sodiumbicarbonate was also carried out by packing the anion exchange resininto a regeneration tower different from the purifier towers and byrepeating 12 times a step comprising downflow of the aqueous regenerantsolution through the tower at a SV of 2.25 hr⁻¹ and at a BV of 0.75L/L-R, discontinuing the passing of the aqueous solution of regenerant,and upflow of ultra-pure water through the tower at a SV of 13.2 hr-¹and at a BV of 0.3 L/L-R. Thereafter, ultra-pure water washing of theanion exchange resin was carried out by repeating 6 times a cyclecomprising downflow of ultra-pure water through the tower at a SV of13.2 hr⁻¹ and at a BV of 3.3 L/L-R and upflow of ultra-pure waterthrough the tower at the same SV and BV. Thus, there was obtained HCO₃⁻-type anion exchange resin.

[0101] The thus regenerated ion exchange resins were packed in the formof a slurry into the respective purifier towers and subjected topractical use.

[0102] After the completion of passing of aqueous hydrogen peroxidesolution through the ion exchange resin towers, the purified aqueoushydrogen peroxide solution having been discharged from the final H⁺-typecation exchange resin tower was sampled and diluted with ultra-purewater from which impurities had been removed to an extremely high degreeso as to adjust the concentration of hydrogen peroxide to 31% by weight.

[0103] The concentrations of metal ion impurities in the thus obtainedpurified aqueous hydrogen peroxide solution were measured by theflameless atomic absorption method and the ICP-MS method. On the otherhand, the concentrations of metal ion impurities in the charged aqueoushydrogen peroxide solution were measured by the flameless atomicabsorption method and the ICP-AES method.

[0104] The results are given in Table 2.

[0105] Exhibited impurity removing level remained unchanged despitecontinuous operation until BV=500 L/L-R corresponding to the end of ionexchange resin life. TABLE 1 Metal impurities in charged aqueoushydrogen peroxide solution Analyzed value Impurities (ppb) Al 770 Cu 0.2Fe 4.5 K 132 Na 15160 Pb 2 Ca 0.6 Mg 0.6

[0106] TABLE 2 Content of metal impurities in obtained purified aqueoushydrogen peroxide solution Measuring Measured Measuring Measured limit(ppt) value (ppt) limit (ppt) value (ppt) Ag 0.5 ND Mg 0.2 ND Al 0.2 0.2Mn 0.3 ND As 2 ND Mo 0.3 ND Au 0.2 ND Na 0.5 ND B 4 ND Nb 0.1 ND Ba 0.1ND Ni 0.7 ND Be 5 ND Pb 0.1 ND Bi 0.2 ND Pd 0.3 ND Ca 2 ND Pt 0.2 ND Cd0.3 ND Sb 0.3 ND Co 1 ND Sn 0.8 ND Cr 1 1   Sr 0.05 ND Cu 0.5 ND Ta 0.1ND Fe 0.5 0.7 Ti 2 ND Ga 0.5 ND Tl 0.1 ND Ge 2 ND V 1 ND In 0.1 ND Zn 2ND K 2 ND Zr 0.1 0.1 Li 0.02 ND

Comparative Example 1

[0107] Charged aqueous hydrogen peroxide solution was purified in thesame manner as in Example 1, except that, referring to FIG. 4, an outletportion of the liquid feed pump was fitted with a bypass with a valvefor regulating the liquid feed, except that the space velocity (Sv) wasset for 15 hr-¹ by the valve at the initial stage, the flow rate notcontrolled thereafter, and except that no level control was effected inthe purifier towers.

[0108] As a result, bubbles slowly began to stick to the anion exchangeresin in the form of bicarbonate ions, so that not only was the flowrate lowered but also a liquid surface rise and pressure increase began.The growth of bubbles led to formation of a shortcut and causeddisordering of ion exchange band. Upon an elapse of BV=75 L/L-R, the SVwas decreased to 5 hr⁻¹, and leakage of Al, Na, etc. began. The aqueoushydrogen peroxide solution was sampled upon an elapse of 8 hr, and thehydrogen peroxide concentration thereof was adjusted to 31% by weight.In the resultant solution, the concentration of Al impurities was 60ppt, and the concentration of Na impurities was 50 ppt.

What is claimed is:
 1. A process for producing a purified aqueoushydrogen peroxide solution, comprising passing a charged aqueoushydrogen peroxide solution containing impurities through a purifiertower packed with an ion exchange resin, a chelate resin or anadsorption resin to thereby purify the charged aqueous hydrogen peroxidesolution, wherein there are provided a feed pump of given output capableof causing the charged aqueous hydrogen peroxide solution to flow to thepurifier tower and further a flow sensor capable of sensing a flow rateof charged aqueous hydrogen peroxide solution being fed to the purifiertower and wherein the output of the feed pump is controlled incooperation with the flow sensor so as to bring the charged aqueoushydrogen peroxide solution into contact with the ion exchange resin,chelate resin or adsorption resin while maintaining the flow of chargedaqueous hydrogen peroxide solution at a constant rate.
 2. The process asclaimed in claim 1, wherein the output of the feed pump for the chargedaqueous hydrogen peroxide solution is controlled by means of aninverter.
 3. The process as claimed in claim 1, wherein the flow rate ofcharged aqueous hydrogen peroxide solution is 5 to 40 hr⁻¹ in terms ofspace velocity.
 4. The process as claimed in claim 1, wherein the flowrate of charged aqueous hydrogen peroxide solution is controlled so thatits variation falls within the range of ±2.5%.
 5. The process as claimedin claim 1, wherein any part brought into contact with the aqueoushydrogen peroxide solution is composed of a fluororesin.
 6. An apparatusfor producing a purified aqueous hydrogen peroxide solution, comprisingat least one purifier tower packed with an ion exchange resin, a chelateresin or an adsorption resin, through which a charged aqueous hydrogenperoxide solution containing impurities is passed so as to effectcontact thereof with the ion exchange resin, chelate resin or adsorptionresin, thereby purifying the charged aqueous hydrogen peroxide solution,which apparatus further comprises: a feed pump of given output capableof causing the charged aqueous hydrogen peroxide solution to flow to thepurifier tower, a flow sensor capable of sensing a flow rate of chargedaqueous hydrogen peroxide solution being fed to the purifier tower bymeans of the feed pump, and a flow control unit capable of controllingthe output of the feed pump on the basis of a detection result of theflow sensor so as to maintain the flow of charged aqueous hydrogenperoxide solution being fed to the purifier tower at a constant rate. 7.The apparatus as claimed in claim 6, wherein the flow control unit is aninverter control unit capable of controlling the output of the feed pumpfor the charged aqueous hydrogen peroxide solution by means of aninverter.
 8. The apparatus as claimed in claim 6, wherein the flowcontrol unit is one capable of controlling the flow rate of chargedaqueous hydrogen peroxide solution being fed to the purifier tower so asto be in the range of 5 to 40 hr⁻¹ in terms of space velocity.
 9. Theapparatus as claimed in claim 6, wherein the flow control unit is onecapable of controlling the flow rate of charged aqueous hydrogenperoxide solution being fed to the purifier tower so that its variationfalls within the range of ±2.5%.
 10. The apparatus as claimed in claim6, wherein any part brought into contact with the aqueous hydrogenperoxide solution is composed of a fluororesin.
 11. The apparatus asclaimed in claim 6, which further comprises a level sensor capable ofdetecting a water level in the purifier tower and a level control unitcapable of maintaining the water of the purifier tower at a constantlevel on the basis of a detection result of the level sensor.
 12. Theapparatus as claimed in claim 6, which further comprises a pressuresensor capable of detecting an internal pressure of the purifier towerand a pressure control unit capable of maintaining an internal part ofthe purifier tower at a constant pressure on the basis of a detectionresult of the pressure sensor.
 13. The apparatus as claimed in claim 12,wherein the pressure control unit is one capable of effecting such acontrol as to carry out not only stopping of the feed pump but alsofeeding of cooling water into the purifier tower on the basis of adetection result of the pressure sensor.
 14. The apparatus as claimed inclaim 6, which further comprises a temperature sensor capable ofdetecting an internal temperature of the purifier tower and atemperature control unit capable of maintaining an internal part of thepurifier tower at a constant temperature on the basis of a detectionresult of the temperature sensor.
 15. The apparatus as claimed in claim14, wherein the temperature control unit is one capable of effectingsuch a control as to carry out not only stopping of the feed pump butalso feeding of cooling water into the purifier tower on the basis of adetection result of the temperature sensor.
 16. The apparatus as claimedin claim 6, which further comprises a strainer arranged at a bottom partof the purifier tower, said strainer comprising a filter and, disposedthereunder, a flange member having at its center a liquid drawoff portand having open grooves disposed substantially in the form of concentriccircles, said open grooves communicating with the liquid drawoff port.17. The apparatus as claimed in claim 6, wherein a plurality of purifiertowers are connected to each other in series.
 18. The apparatus asclaimed in claim 6, wherein a plurality of purifier towers are connectedto each other in series, and the flow sensor and the flow control unitare arranged at a line for feeding the charged aqueous hydrogen peroxidesolution to the first purifier tower.
 19. The process as claimed inclaim 2, wherein the flow rate of charged aqueous hydrogen peroxidesolution is 5 to 40 hr⁻¹ in terms of space velocity.
 20. The process asclaimed in claim 2, wherein the flow rate of charged aqueous hydrogenperoxide solution is controlled so that its variation falls within therange of ±2.5%.
 21. The process as claimed in claim 3, wherein the flowrate of charged aqueous hydrogen peroxide solution is controlled so thatits variation falls within the range of ±2.5%.
 22. The process asclaimed in claim 2, wherein any part brought into contact with theaqueous hydrogen peroxide solution is composed of a fluororesin.
 23. Theprocess as claimed in claim 19, wherein any part brought into contactwith the aqueous hydrogen peroxide solution is composed of afluororesin.
 24. The process as claimed in claim 21, wherein any partbrought into contact with the aqueous hydrogen peroxide solution iscomposed of a fluororesin.
 25. The apparatus as claimed in claim 7,wherein the flow control unit is one capable of controlling the flowrate of charged aqueous hydrogen peroxide solution being fed to thepurifier tower so as to be in the range of 5 to 40 hr¹ in terms of spacevelocity.
 26. The apparatus as claimed in claim 7, wherein the flowcontrol unit is one capable of controlling the flow rate of chargedaqueous hydrogen peroxide solution being fed to the purifier tower sothat its variation falls within the range of ±2.5%.
 27. The apparatus asclaimed in claim 8, wherein the flow control unit is one capable ofcontrolling the flow rate of charged aqueous hydrogen peroxide solutionbeing fed to the purifier tower so that its variation falls within therange of ±2.5%.
 28. The apparatus as claimed in claim 25, wherein anypart brought into contact with the aqueous hydrogen peroxide solution iscomposed of a fluororesin.
 29. The apparatus as claimed in claim 27,wherein any part brought into contact with the aqueous hydrogen peroxidesolution is composed of a fluororesin.
 30. The apparatus as claimed inclaim 28, which further comprises a level sensor capable of detecting awater level in the purifier tower and a level control unit capable ofmaintaining the water of the purifier tower at a constant level on thebasis of a detection result of the level sensor.
 31. The apparatus asclaimed in claim 29, which further comprises a level sensor capable ofdetecting a water level in the purifier tower and a level control unitcapable of maintaining the water of the purifier tower at a constantlevel on the basis of a detection result of the level sensor.
 32. Theapparatus as claimed in claim 30, which further comprises a pressuresensor capable of detecting an internal pressure of the purifier towerand a pressure control unit capable of maintaining an internal part ofthe purifier tower at a constant pressure on the basis of a detectionresult of the pressure sensor.
 33. The apparatus as claimed in claim 31,which further comprises a pressure sensor capable of detecting aninternal pressure of the purifier tower and a pressure control unitcapable of maintaining an internal part of the purifier tower at aconstant pressure on the basis of a detection result of the pressuresensor.
 34. The apparatus as claimed in claim 13, which furthercomprises a temperature sensor capable of detecting an internaltemperature of the purifier tower and a temperature control unit capableof maintaining an internal part of the purifier tower at a constanttemperature on the basis of a detection result of the temperaturesensor.
 35. The apparatus as claimed in claim 15, which furthercomprises a strainer arranged at a bottom part of the purifier tower,said strainer comprising a filter and, disposed thereunder, a flangemember having at its center a liquid drawoff port and having opengrooves disposed substantially in the form of concentric circles, saidopen grooves communicating with the liquid drawoff port.
 36. Theapparatus as claimed in claim 16, wherein a plurality of purifier towersare connected to each other in series.
 37. The apparatus as claimed inclaim 17, wherein a plurality of purifier towers are connected to eachother in series, and the flow sensor and the flow control unit arearranged at a line for feeding the charged aqueous hydrogen peroxidesolution to the first purifier tower.